Method and system for linearizing an amplifier using transistor-level dynamic feedback

ABSTRACT

The present disclosure describes a method and system for linearizing an amplifier using transistor-level dynamic feedback. The method and system enables nonlinear amplifiers to exhibit linear performance using one or more of gain control elements and phase shifters in the feedback path. The disclosed method and system may also allow an amplifier to act as a pre-distorter or a frequency/gain programmable amplifier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/332,682, filed on Oct. 24, 2016, which is a continuation-in-part ofU.S. patent application Ser. No. 14/575,373, filed on Dec. 18, 2014,which claims the benefit of and priority to U.S. Provisional PatentApplication Ser. No. 61/929,015, filed on Jan. 18, 2014, the disclosuresof which are incorporated herein in their entireties by reference.

BACKGROUND Field of the Invention

The present disclosure relates to a method and system for linearizingthe performance of amplifiers using transistor-level dynamic feedback.

Description of the Related Art

Amplifiers are often treated as linear devices that amplify an inputsignal via a constant gain factor. It is well understood in the art thatamplifiers often possess nonlinear performance above a certain thresholdof input power. For example, as the power level of an input signalincreases above such a threshold, an amplifier's ability to provide gainwill often increasingly degrade. This can result in a distorted outputsignal from the amplifier due to the low-power elements of the inputsignal having been amplified with a higher gain factor than thehigh-power elements of the input signal.

One solution to avoiding nonlinear performance in an amplifier is torestrict input signals to below the threshold where such signals wouldinduce nonlinear distortions. However, this may be undesirable as such arestriction limits the power efficiency that can be obtained when usingsuch an amplifier.

Another approach in the prior art is to use a pre-distortion circuitprior to the amplifier to correct for the nonlinear distortions of theamplifier. For example, if a non-linear amplifier has a gain profilecharacterized by the function y=√{square root over (x)}, then using apre-distortion circuit prior to the amplifier with a gain profilecharacterized by the function y=x² should result in linear performance(i.e., y=x). The problem with this approach is that it often createsunwanted intermodulation distortion byproducts that arise from small butsignificant mismatches between the pre-distortion circuit and thenonlinear profile of the amplifier. Such mismatches often occur for avariety of reason, such as the pre-distortion circuit and the amplifierbeing influenced by environmental factors (e.g., temperature, humidity,or supply voltage fluctuations) or the slow degradation of these devicesover time. Another problem with pre-distortion circuits is that theytypically consume considerable power. In addition, they often requirehighly complex and costly designs as they must operate at often veryhigh frequencies and also provide a very high operating bandwidth sothat intermodulation distortion byproducts can be canceled out withinthe amplifier.

SUMMARY

One aspect of the invention is directed to a method, system, apparatus,or media for performing amplification of an input signal using dynamicfeedback. For example, in one embodiment, an amplifier may be adapted toamplify the input signal by a gain factor. A feedback path may becoupled to an output and an input of the amplifier for conveying afeedback signal from an output signal of the amplifier to the input ofthe amplifier. The feedback path may include one or more gain controlelements for adjusting the magnitude of the feedback signal and acontroller may be coupled to the input of the amplifier (prior to thefeedback path) and further coupled to the one or more gain controlelements. In such an embodiment, the controller may be adapted to applycontrol voltages to the one or more gain control elements, such that theamplifier may provide a constant gain factor and a constant relativephase shift over a previously nonlinear operating range of the amplifierwithout dynamic feedback.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a circuit 100 for performing signal amplificationwith dynamic feedback.

FIG. 2 illustrates a circuit 200 that may be implemented for performingsignal amplification with dynamic feedback.

FIG. 3 shows an example of a methodology that illustrates how one mayfind the control voltages for gain or phase adjustments.

FIG. 3A shows an example of a gain profile for an amplifier withoutdynamic feedback.

FIG. 3B shows an example of relative phase shift profile for anamplifier without dynamic feedback.

FIG. 4 shows an example of the gain of an amplifier for a given inputsignal based on variation of a control voltage applied to a gain controlelement.

FIG. 5 shows an example of the control voltages required for givenoutput power back offs to achieve a desired constant gain level.

FIG. 6A shows an example of a corrected gain profile for an amplifierwith dynamic feedback.

FIG. 6B shows an example of a corrected relative phase shift profile foran amplifier with dynamic feedback.

FIG. 7 shows an example of the presence of intermodulation distortionbyproducts using an amplifier with and without dynamic feedback.

FIG. 8 illustrates an example of using circuit 200 as a pre-distorterfor a subsequent nonlinear amplifier.

FIG. 9A shows an example of a desired gain profile of a pre-distorter.

FIG. 9B shows an example of the actual gain profile obtained for apre-distorter using circuit 200.

FIG. 10 shows an example of a corrected gain profile for a signalapplied to a pre-distorter and amplifier.

FIG. 11 shows an example of the presence of intermodulation distortionbyproducts using an amplifier with and without a pre-distorter.

FIG. 12 shows an example of how a gain control element in the feedbackpath may be adjusted to increase or decrease gain of an amplifier at aspecific frequency.

FIG. 13 shows an example of how a phase shifter in the feedback path maybe adjusted to shift the gain profile of an amplifier across a frequencyspectrum.

FIG. 14 illustrates a circuit 1400 for performing signal amplificationwith dynamic feedback.

FIG. 15 shows an example of signal modulation.

FIG. 16A shows an example table of the control voltages required forgiven output power back offs to achieve a desired constant relativephase shift.

FIG. 16B shows an example chart of the control voltages required forgiven output power back offs to achieve a desired constant relativephase shift.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 shows an example of a circuit 100 for performing signalamplification. In circuit 100, amplifier 106 may be used to amplifyinput signals received via input port 102. The amplified signal may bereceived via output port 104. It is well known in the art thatamplifiers often possess a linear range for amplification. For example,if input signals received by amplifier 106 via input port 102 are withinsuch a linear range, then the amplified signal received via output port104 will remain in linear proportion to the input signals (e.g., y=Gx,where y is the output signal, x is the input signal, and G is a constantgain factor supplied by amplifier 106). However, if such input signalsexceed the linear range of amplifier 106, then the amplified signalreceived via output port 104 may exhibit nonlinear distortions.

For example, one nonlinear distortion is gain compression. As an inputsignal increases above the linear range, the ability of an amplifier toamplify the signal by a constant gain factor will increasingly degrade.Another example of nonlinear distortion is phase rotation. As an inputsignal increases above the linear range, the ability of an amplifier tomaintain the correct relative phase of the signal will increasinglydegrade in relation to lower power input signals. These and othernonlinear distortions can substantially degrade the performance ofamplifier 106, such that the use of bandwidth-efficient signalingschemes may become considerably impaired. While ensuring that inputsignals to amplifier 106 stay within the linear range of amplifier 106avoids any nonlinear distortions, it also reduces the power efficiencyof amplifier 106 compared to that of an ideal amplifier that exhibitsonly linear performance.

FIG. 2 shows an example of a circuit 200 that may used to implementcircuit 100 and thus may provide for transistor-level dynamic feedback.In circuit 200, a feedback path may be added between input port 202 andoutput port 204. Such a feedback path may be composed first oftransistor 214 connected to output port 204 through capacitor 226.Resistance control port 206 may be connected to the gate terminal oftransistor 214 for applying a control voltage. By varying the controlvoltage applied via resistance control port 206, transistor 214 may actlike a gain control element in the feedback path, thereby allowing foradjusting the gain factor of transistor 212. It should be appreciatedthat when a transistor is used in passive mode (meaning that it hasalmost equal voltage on its drain and source), it may act like aresistor connected between the drain and source terminals. The value ofthe resistor may be set using the gate voltage (relative to thedrain/source terminals). Additionally, one may connect multipleresistors in series to obtain higher values of resistance. In the samemanner, one may connect multiple passive transistors in series to obtaina larger value of resistance. In that case, each series transistor maybe controlled independently through its resistance control port (e.g.,its gate terminal). Hence, transistor 214 which may be controlledthrough port 206 may be replaced with a set of series transistors eachhaving its own resistance control port. Having multiple resistancecontrol ports may give higher flexibility in controlling the gain oftransistor 212.

From transistor 214, the feedback path may continue through capacitor224 to phase control port 208. Phase control port 208 may be connectedto the gate terminal of transistor 216 for applying a control voltage.By varying the control voltage applied via phase control port 208,transistor 216 may act like a variable capacitor in the feedback path,thereby allowing for adjusting the relative phase shift of transistor212. In circuit 200, transistor 216 may have its drain and sourceterminals connected to ground 210. From phase control port 208, thefeedback path may continue through an RLC circuit to input port 202. Anexample of such an RLC circuit is shown with inductor 218, resistor 220,and capacitor 222 connected in series. In circuit 200, the transistorgate bias may come through port 248 which may have a series resistor(246) to isolate the gate bias from the signal (RF) path. Additionally,drain bias may come through port 252 which may have a series inductor(250) to isolate the drain bias from the signal (RF) path. In addition,the input power may be sensed at port 232 through coupler 230. Theoutput power may be sensed at port 228 through coupler 226. A gain/phasecontroller (234) may have inputs and outputs. The inputs may include oneor more of the input power (such as sensed at port 236 of thecontroller), the output power (such as sensed at port 238 of thecontroller), and environmental signals such as temperature and humidity(such as sensed at port 240 of the controller). The gain/phasecontroller (234) may have one or more outputs, such as 242 and 244,which may drive the phase control (208) and resistance control (206) toachieve the desired performance.

Gain/phase controller 234 may contain software or hardware forperforming the functions described herein, such as methodology 300. Forexample, gain/phase controller 234 may contain one or more processorsand memory. Gain/phase controller 234 may be implemented by a variety ofdevices, such as digital signal processors, FPGA, custom ASICs, PICs,etc.

With respect to circuit 200 described above, an input signal (e.g., QAM,QPSK) may be applied to input port 202. Transistor 212 then may amplifythe output signal, a portion of which may be sent back via the feedbackpath as a feedback signal. Depending on the state of the input signal,the feedback signal may result in positive or negative feedback thatadjusts the gain factor or relative phase shift of the input and outputsignals of transistor 212. By adjusting the voltages applied toresistance control port 206 or phase control port 208, the amount ofattenuation and capacitance in the feedback path can be adjusted,thereby allowing for the gain factor and relative phase shift betweenthe output (at 204) and the input (at 202) of transistor 212 to be heldconstant for all power levels of an input signal. Consequently, controlvoltages applied to resistance control port 206 or phase control port208 may be adjusted for each power level of the input signal such thatsmall and large signal inputs experience a similar response fromtransistor 212. This allows for a linearized operation of transistor 212through dynamic feedback control and may prevent the generation ofunwanted intermodulation distortion byproducts (e.g., third-orderintermodulation distortion).

FIG. 3 shows a methodology 300 for constructing a lookup table for amodulation signal of a specific power level that may be applied tocircuit 100. At step 302, gain control element 108 of circuit 100 may beset to its maximum resistance setting via resistance control port 110.At step 304, phase shifter 112 of circuit 100 may be set to its minimumphase shift setting via phase control port 114. At step 306, a modulatedsignal (e.g., QPSK, 16 QAM) having a specific power level may be appliedto input port 102 of circuit 100. At step 308, the modulated signalafter amplification may be measured at output port 104 in order toobtain a complex transfer function describing the behavior of theamplifier. This complex transfer function may be represented for exampleas a gain factor and relative phase shift. If variable resister 108 isset to its maximum resistance setting and phase shifter 112 is set toits minimum phase shift setting, this complex transfer functiondescribes the performance of the amplifier without feedback for themodulated signal having a specific power level.

To characterize the performance of the amplifier with feedback for themodulated signal having a specific power level, methodology 300 mayproceed to step 310 where gain control element 108 may be adjusted to anew value. In addition, methodology 300 may proceed to step 312 wherephase shifter 112 may be adjusted to a new value. Once gain controlelement 108 or phase shifter 112 is set to a new value, methodology 300may return to step 306 as described above. If the new setting(s) forgain control element 108 or phase shifter 112 do not result in thedesired complex transfer function, then steps 308 through 312 may berepeated until optimum settings for gain control element 108 or phaseshifter 112 are obtained. Once such optimum settings are found, they maybe recorded at Step 314. In some embodiments, recording the settings mayinclude the power level of the input signal. Moreover, methodology 300may be repeated using an input power signal at different power levels toconstruct a lookup table using the information recorded at step 314.

FIGS. 3A and 3B show examples of an amplifier's gain and phase profilesusing circuit 200. Both figures were obtained by setting the gaincontrol element (in the form of transistor 214) to maximum resistanceand the phase shifter (in the form of transistor 216) to minimum phaseshift and applying a 1 GHz continuous wave modulated signal at differentpower levels. FIG. 3A shows that the gain factor of the amplifiergradually increases from −20 dB to −5 dB output power back off. Between−5 dB and 0 dB output power back off, the gain factor of the amplifierseverely degrades. FIG. 3B shows the relative phase shift induced by theamplifier from −20 dB to 0 dB output power back off. While some systemsmay be able to tolerate a small amount of phase shift induced by anamplifier, FIG. 3B shows that as input power approaches 0 dB outputpower back off the relative phase shift becomes more severe.

Methodology 300 may be used to linearize such an amplifier with thecharacteristics shown in FIGS. 3A and 3B. For example, aftercharacterizing the behavior of the amplifier as shown in FIGS. 3A and3B, one may decide to linearize the performance of the circuit from −20dB to 0 dB output power back off. In terms of gain, the amplifier'suncorrected lowest gain factor shown in FIG. 3A is 7.7 dB at 0 dB poweroutput back off. Thus, one may decide to linearize the amplifier across−20 dB to 0 dB output power back off to provide a constant gain level of7.7 dB. However, should one decide to operate the amplifier in adifferent range (e.g., −20 dB to −5 dB output power back off), theuncorrected lowest gain factor in such a range would be considerablyhigher, thus allowing for a higher constant gain factor (around 10 dB)within that range. Accordingly, it should be understood that the methodsand systems described herein can be adapted to a variety of differentranges of input power to achieve different gain factors.

In accordance with methodology 300, settings for the gain controlelement may be determined for a given input power to obtain the desiredoutput power. For example, FIG. 4 shows the amplifier gain for acontinuous wave modulated signal at input power of −20 dB output powerback off as the gain control element of circuit 200 is varied via avarying control voltage. FIG. 4 shows that applying a control voltagebetween 0 V to −5 V causes the amplifier's gain to vary from around 10dB to slightly over 4 dB. To achieve a gain factor of 7.7 dB for theinput signal at −20 dB output power back off, FIG. 4 shows that acontrol voltage of −2.125 V for the gain control element is required.This process can be repeated for input signals at a variety of powerlevels (e.g., −19 dB, −18 dB, −17 dB, . . . , 0 dB output power backoff) to obtain respective control voltages to maintain a constant gainof 7.7 dB at different power levels. For example, FIG. 5 shows a graphof control voltages to be applied to the gain control element as theinput signal varies from −20 dB to 0 dB output power back off.

In a similar fashion to the process above, control voltages for thephase shifter can also be determined for input signals at a variety ofpower levels to maintain a desired relative phase shift. For example,FIG. 16A shows the control voltages that may be used to achieve a 0degree relative phase shift using circuit 200 as above, which wasobtained via methodology 300. These control voltages that may be usedwith the phase shifter of circuit 200 are graphed in FIG. 16B.

After determining the appropriate control voltages for an input signaloperating within a certain range of output power back off, these controlvoltages can be applied to the resistance control port and the phasecontrol port to linearize the performance of the transistor. Forexample, control voltages obtained using the processes described abovecan be used to linearize the performance of the amplifier described inaccordance with FIGS. 3A and 3B. The result of using such controlvoltages with such an amplifier is shown in FIGS. 6A and 6B. FIG. 6Ashows that the corrected gain of the amplifier is now relativelyconstant at 7.7 dB over the range of 0 dB to −20 dB output power backoff. FIG. 6B shows that the corrected relative phase shift of theamplifier is now relatively constant at 0 degrees over the range of 0 dBto −20 dB output power back off. In addition to corrected gain factorand relative phase shift, FIG. 7 shows that the methods described hereinresult in improved suppression of intermodulation distortion byproductions. The dotted line is the spectrum of an output signal when anamplifier is operated without feedback (e.g., setting the gain controlelement to maximum resistance and the phase shifter to minimum phaseshift). The solid line is the spectrum of an output signal when theamplifier is operated using feedback as disclosed herein. The use ofcontrol voltages to a gain control element or phase shifter to shape afeedback signal may require transistors with a fast response rate. Forexample, for an RF or microwave signal with a 10 MHz modulation signal(time constant equivalent to 100 ns), an amplifier's characteristics maychange at a 100 ns time scale. Consequently, in order to use controlvoltages determined by methodology, transistors which can respond fasterthan the time in which an amplifier's characteristics may change may berequired.

In some embodiments, the methods and systems disclosed herein may beused to implement a pre-distorter. For example, circuit 200 may beimplemented as shown in FIG. 8 prior to an amplifier 802 (shown in theform of transistor Q). If amplifier 802 has the characteristics asdescribed with respect to FIGS. 3A and 3B, then one may wish to use apre-distortion circuit with the gain profile shown in FIG. 9A tocompensate for variations in the gain profile of amplifier 902. Usingthe methods and systems described above, control voltages for a desiredgain profile (e.g., the gain profile shown in FIG. 9A) may be determinedfor the desired range of input power. FIG. 9B shows an example of theactual gain profile of circuit 200 after such control voltages have beendetermined. By cascading circuit 200 as a pre-distorter prior toamplifier 802 and using such control voltages, nearly constant gainlevel using these two elements can be achieved as shown in FIG. 10. In asimilar fashion, the pre-distortion technique disclosed herein can beused to determine and utilize control voltages for obtaining a desiredrelative phase shift profile.

In addition to corrected gain and relative phase shift, FIG. 11 showsthat the use of circuit 200 as a pre-distorter may result in improvedsuppression of intermodulation distortion by productions. The dottedline is the spectrum of an output signal when an amplifier (902) isoperated without pre-distortion as described herein. The solid line isthe spectrum of an output signal when amplifier 902 is operated withpre-distortion as described herein.

In some embodiments, the methods and systems disclosed herein may beused for providing a frequency/gain programmable amplifier. For example,circuit 100 (or circuit 200) may be adjusted via a phase shifter in thefeedback path (e.g., phase shifter 112) such that the path length of thefeedback path varies. Adjusting the path length may be used to determinethe phase of the feedback signal when it combines with the input signal.For example, if the feedback path is selected such that the phase of thefeedback signal upon combination with the input signal is 360 degrees,this will result in positive feedback. Alternatively, if the feedbackpath is selected such that the phase of the feedback signal uponcombination with the input signal is 180 degrees, this will result innegative feedback. In addition, by increasing or decreasing theresistance of a gain control element in the feedback path (e.g., gaincontrol element 108), the magnitude of any positive or negative feedbackcan be adjusted. Consequently, for an input signal with a givenfrequency, control voltages may be determined and used herein toincrease or decrease the gain of an amplifier (e.g., amplifier 106).

For example, FIG. 12 shows a situation where a control voltage wasapplied to phase shifter 112 so that feedback path length was optimizedfor a 12 GHz input signal (i.e., the path length of the feedback pathwas 360 degrees for a 12 GHz signal). In addition, FIG. 12 shows theeffect of setting the gain control element to three different levels ofresistance, thereby changing the magnitude of the feedback signal. Inthe situation where the control voltage was set to induce the gaincontrol element to a low resistance, the gain of the amplifier can beseen to be around 18 dB, while control voltages that corresponded tohigher resistance settings resulted in lower gain. FIG. 13 shows howadjusting the control voltage applied to a phase shifter in the feedbackpath shifts the gain profile of the amplifier in terms of frequency forthree different settings. Consequently, using the methods and systemsdescribed above, control voltages may be determined and used to providea specific gain for an input signal at a particular frequency.

In some embodiments, the feedback may be implemented using two gaincontrol elements, instead of gain and phase control elements. Circuit1400, shown in FIG. 14, shows such an example of such an implementation.The input signal may enter through port 1402, may be amplified bytransistor 1406, and may exit at port 1404. Part of the output signal(at 1404) may be fed back to the input through a feedback path where itmay be split equally between two branches (1408 and 1410). Branch 1410may act on the original signal (the so-called I-component of thesignal), while branch 1408 has a 90 degree phase shift (1412) and mayact on the 90-degree-shifted signal (the so-called Q-component of thesignal). In branch 1410, the amplitude of the I-signal may be controlledusing a gain control element (1416), while in branch 1408, the amplitudeof the Q-signal may be controlled using a gain control element (1414).Afterwards, the I-signal may be shifted by a 90 degree shift (1412) andmay exit at 1420, while the Q-signal may exit at 1418 without furtherphase shifts. Then, the I-signal and Q-signal may be combined and phaseshift 1422 may be added, after which the signal may be combined with theinput signal (at 1402) prior to transistor 1406. A direct relationshipbetween gain/phase variations and I/Q variations can be obtained by thisapproach. Mathematically, one can write:

Acos(2πft+φ)=Acos(2πft)cos(φ)−Asin(πft)sin(φ)

defining I and Q as

I=Acos(φ)

Q=−Asin(φ)=Acos(φ+π/2)

Then

Acos(2πft+φ)=Icos(2πft)+Qsin(2πft)

Hence, one may represent a gain/phase variation as an I/Q variation.Methodology 300 may then be used to find control voltages for the gaincontrol elements of circuit 1400. Circuit 1400 may include a controllerfor performing methodology 300.

In some embodiments, the methods and systems disclosed herein may beused to implement a modulator. A modulator may impose a varying phaseand amplitude on an input signal exhibiting a constant amplitude andphase. For example, circuit 100 (or circuit 200) may be adjusted via aphase shifter in the feedback path (e.g., phase shifter 112) or adjustedvia a gain control element in the feedback path (e.g., gain controlelement 108) to impose a phase shift or an amplitude change on an inputsignal exhibiting a constant amplitude and phase. As an example, circuit200 was driven with a constant input signal while the phase control wasdriven by QPSK signal. FIG. 15 shows the resulting signal constellationdiagram received at output port 204.

It is to be understood that the methods and systems described herein canbe used for a variety of input signals (e.g., QPSK, QAM). In addition,the table lookup of control voltages to be applied to the resistancecontrol port and phase control ports can be determined and utilizedusing additional factors beyond output power back-off, such as thetemperature of the amplifier, the length of time the amplifier has beenoperating, the prior state(s) of the input signal at a fixedinterval(s), etc. These may be determined using methodology 300, such asvia a controller, by additionally adjusting such parameters.Consequently, tables may be constructed that allow, such as via acontroller, application of a control voltage to a gain control elementor phase shifter based on such parameters.

In some embodiments, the total physical length of the feedback path maybe constrained to less than the highest wavelength of the maximumoperating frequency present in the feedback path. For example, if themaximum operating frequency present in the feedback path is 60 GHz, thetotal physical length of the feedback path may be constrained to 5 mm orless. In other embodiments, the total physical length of the feedbackpath may be constrained to an integer multiple of the highest wavelengthof the maximum operating frequency present in the feedback path. Forexample, if the maximum operating frequency present in the feedback pathis 60 GHz, the total physical length of the feedback path may beconstrained to 5 mm, 10 mm, 15 mm, etc. In yet other embodiments, thetotal physical length of the feedback path may be constrained to afractional multiple of the highest wavelength of the maximum operatingfrequency present in the feedback path. For example, if the maximumoperating frequency present in the feedback path is 60 GHz, the totalphysical length of the feedback path may be constrained to 2.5 mm (halfthe wavelength of the 60 GHz signal).

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated. Forexample, one skilled in the art will understand that a variety ofdifferent transistors or other elements may be used to implement anamplifier using a dynamic feedback path as disclosed herein (e.g., again control element may be implemented using variable resistors,variable capacitors, inductors, active semiconductor devices, etc.). Inaddition, those skilled in the art will understand that a variety ofdifferent feedback paths may be used in accordance with the abovedisclosure. For example, methodology 300 may be used in any one or morefeedbacks path where gain control elements or phase shifters allow forthe adjustment of the phase and magnitude of the feedback signal. It isintended that the following claims be interpreted to embrace all suchvariations and modifications.

What is claimed is:
 1. A method for performing amplification of an inputsignal using dynamic feedback comprising: receiving an input signal,wherein the input signal is applied to an input of an amplifier;receiving an output signal, wherein the output signal is obtained froman output of an amplifier; applying one or more control voltages to oneor more gain control elements for adjusting the magnitude of a feedbacksignal, wherein the one or more gain control elements are contained inone or more feedback paths coupled to an output and an input of theamplifier for conveying the feedback signal from an output signal of theamplifier to the input of the amplifier; limiting the feedback signal tohave a maximum operating frequency whose wavelength is equal to or lessthan the one or more feedback paths' physical length; and using valuesfor the one or more control voltages for implementing a programmablevariable gain amplifier.
 2. A method for performing amplification of aninput signal using dynamic feedback comprising: receiving an inputsignal, wherein the input signal is applied to an input of an amplifier;receiving an output signal, wherein the output signal is obtained froman output of an amplifier; applying a first set of one or more controlvoltages to one or more gain control elements for adjusting themagnitude of a feedback signal, wherein the one or more gain controlelements are contained in one or more feedback paths coupled to anoutput and an input of the amplifier for conveying the feedback signalfrom an output signal of the amplifier to the input of the amplifier;limiting the feedback signal to have a maximum operating frequency whosewavelength is equal to or less than the one or more feedback paths'physical length; and applying a second set of one or more controlvoltages to one or more phase shifters for adjusting the phase of afeedback signal, wherein the one or more phase shifters are contained inone or more feedback paths, wherein applying the second set of one ormore control voltages to one or more phase shifters allows for adjustingthe phase of a feedback signal for applying predistortion to the inputsignal.
 3. A method for performing amplification of an input signalusing dynamic feedback comprising: receiving an input signal, whereinthe input signal is applied to an input of an amplifier; receiving anoutput signal, wherein the output signal is obtained from an output ofan amplifier; applying a first set of one or more control voltages toone or more gain control elements for adjusting the magnitude of afeedback signal, wherein the one or more gain control elements arecontained in one or more feedback paths coupled to an output and aninput of the amplifier for conveying the feedback signal from an outputsignal of the amplifier to the input of the amplifier; limiting thefeedback signal to have a maximum operating frequency whose wavelengthis equal to or less than the one or more feedback paths' physicallength; and applying a second set of one or more control voltages to oneor more phase shifters for adjusting the phase of a feedback signal,wherein the one or more phase shifters are contained in one or morefeedback paths, wherein applying the second set of one or more controlvoltages to one or more phase shifters allows for adjusting the phase ofa feedback signal for implementing an amplifier with a specific gain ata particular frequency.